Underground steam pipe systems are very necessary in most cities. These systems provide heat and energy to commercial and residential spaces alike. The pipe through which the steam flows can range anywhere from two to twenty-four inches in diameter and is typically made of steel. When steam passes through the steel pipe, the temperature of the pipe rises to 350.degree.-450.degree. F. Because metal is a good conductor of heat, a significant amount of heat would be expected to be dissipated or lost through the pipe, resulting in inefficiency. Therefore, in order to reduce heat dissipation, steel steam pipe is insulated when it is installed.
Foamed plastics are often used, for insulation purposes, at temperatures of up to 120.degree. C., because of their low density, low thermal conductivity and resistance to moisture. Foamed polyurethane, for example, has an aged thermal conductivity of 0.016 W/m.multidot.K at 23.degree. C. Other foamed plastics include polystyrene, polyvinyl chloride (PVC), and phenolic foams. These foamed plastics are "cured" or "cast" and are transformed into rigid structures. Objects of various shapes can be made simply by casting the foam inside a mold which is shaped to make the desired article. For steam pipe insulation applications, foamed plastics are transformed or "precast" into rigid half-cylinders or blocks. These half-cylinders are inserted into the annular area between the steel steam pipe and concrete or tile conduit. According to current practice, this process must necessarily be done before or during laying the pipe underground.
After a period of time and from constant exposure to high temperature, the insulation degrades and deteriorates. When this happens, insulating properties are lost and heat is dissipated through the steel pipe. Therefore, it becomes necessary to repair or reinsulate the pipe to return the steam system to its proper efficiency.
At present, there are a large number of underground steam pipe systems that were installed fifty to sixty years ago. Typically, this steam pipe was insulated when it was installed. For example, the metal pipe was laid inside of either concrete or tile conduit pipe. As further insulation, rigid plastic foam was fit in the two to six inch wide annular space between the steel pipe and the conduit pipe. After the forty to fifty years of continuous use that these steam systems have endured, the original insulation has either disintegrated or has become severely reduced in effective thickness to provide the thermal insulation that is required. Without insulation, a steam line at 350.degree. to 450.degree. F. will lose heat as the steam travels from the plant to the customer. This loss in heat results in the formation of condensate (water) that is then removed from the system through low drain points and steam traps located throughout the system. The efficiency loss due to the excessive condensate formation results in increased costs due to the fuel costs and the loss of chemicals added to the water at the plant making steam.
Also, over the course of fifty years or so, the original insulation decomposes from heat and age; the conduit cracks; ground water removes the original insulation and retrofitting becomes necessary. Thus, there is a need for a cost efficient method to retrofit existing underground steam pipe with new insulation.
Excavation, opening up the conduit, removing and replacing the insulation, while expensive, is generally the only procedure that produces acceptable results. Moreover, re-insulating the underground steam pipe entails numerous problems. First, the ground above the pipe must be removed in order to permit access to the pipe. This involves destroying sidewalks, roads and other structures that are costly to repair or replace after the work is completed. Second, the concrete conduit must be destroyed and replaced with new conduit. The pipes themselves must be removed in order to be retrofitted with new rigid foam insulation. Finally, the pipe must be repositioned underground. The current method is time-consuming as only short sections of pipe can be worked on at a time. As will be appreciated, the complete procedure requires a great expense in materials and labor, not to mention the cost and inconvenience caused by lack of service while the procedure is underway, since it is necessary to shut down the system. Even once the system is shut down, it can take an additional several days to cool sufficiently. Some companies have tried retrofitting with cementations boiler refractory material, but found the material too costly and lacking in performance. Until now, there was no alternative but to accept the heat loss and resulting additional cost.